In the related art, a collision avoidance assistance device for preventing a collision of a vehicle with an obstacle during driving of the vehicle has been developed. For example, in Patent Literature 1, a technology is disclosed, in which a possibility of a collision between an object detected by object detection means and a vehicle is determined for each discrete time, and collision avoidance assistance such as braking assistance is performed according to a result of calculating the possibility of collision which is based on a time to collision (TTC: a time until arrival at the obstacle).